Looking at the calcium math from an even more interesting angle, @KsKingBee if you are feeding a dozen eggs to around 100 birds, that's about 1/10 of an eggshell per bird.
Cool! Chemistry AND math in one question, yaay!
So a little internet searching suggests that the eggshell itself is about 95% calcium carbonate, good old CaCO3. One source said eggshell powder is about 39% elemental calcium (so the other approximately 60% is going to be the carbonate fraction).
If you weigh your eggshells (you only have to do this once, approximations will be close enough), then multiply by 0.4, that will be the approximate weight of the calcium. My guess is that when you then divide that weight in grams by the weight in grams of the amount of feed you are giving your flock at that feeding (don't include the weight of the water, though), you are going to find you have a very small number. Just guessing, but I'm thinking the number of grams in a dozen eggshells compared to the weight of feed for what, around 100 birds(?) is going to be much less than 1%.
In other words, do the math one time, but I bet the difference in the amount of added calcium is less than the "slop" in the label calcium content of "between 2 - 3 %" from the bag.
Does that help?
I betcha @Birdrain92 can do the chemistry precisely, too!
Favorite two subjects! USDA Large egg ways 2 ounces. I think that's with everything in it, not sure. Let's just say that's the egg shell weight to make things simple. It takes 16 ounces to make a one pound. Just to make things simple lets keep it in lbs. since that's what most feed bags are in, or at least in my area. If 40% of an eggshell is calcium itself than we multiply 2 ounces to 0.4. So that means 0.8 ounces of the eggshell is calcium. Lets say you have a 50lb bag of feed. For a daily life of peafowl they need roughly 2% calcium. For a peahen laying I think it would be maybe 3.5% calcium for a good quality egg shell and healthy peahen. To figure this out you would multiple 0.035 to 50 which equals 1.75. That means 1.75lbs of the 50lbs is pure calcium. We need to get it to ounces to make it on similar playing field. So we multiple 1.75 to 16. That way it's in ounces, which equals, 28 ounces of calcium. 40% of an egg shell is calcium. So we need to divide to get to the weight of egg shells in the feed, 70 ounces of egg shells. The reason why we divided is because we multiplied to go from egg shell weight to weight of calcium. To go backwards we have to divide. Then we divide that number by 2. That means there are 35 eggshells in that 50lb bag of feed in our scenario. To double check we can take 50 times it by 16 to get it into ounces. 800 ounces. Take 28 and divide it 800 and you come up with 0.035 which equals 3.5% calcium. It you wish to double check that you got the right percentage, take the weight of the nutrient itself and divide it by the weight of all the feed. The ironic part is we just had a test over make rations in my college Animal Science class. I hope this wasn't too confusing. Next thing I can teach you all is how to do Pearson squares.
Well, except for the part of grossly over-estimating the calcium... the egg shell weight is much less than the weight of the liquid contents. So instead of 2 ounces times 0.4, it's gonna be less than 1/4 ounce times 0.4. (I just weighed a chicken egg shell -- slightly damp with the membrane inside, it was 7 grams.) There aren't 0.8 ounces of shell IN an egg shell. 0.4 x 7 grams is 2.8 grams, or 2800 milligrams of calcium, which is still an overestimate since I didn't dry the shell or peel out the membrane.
@KsKingBee's birds are getting about 1/10 of an eggshell each per day, or something less than 280 mg of elemental calcium per bird, in addition to the amount of calcium in the feed already. That's about as much calcium as in a glass of milk, or as much calcium as in 4 crickets.
Hens lay a whole pea-egg's worth of calcium every other day during laying season -- in addition to the other ways they use up calcium, they are excreting that much more in their own shells. So they excrete more than five times as much calcium per day as would be added.
A dozen chicken eggs would have less than 34 grams of calcium (that's roughly an ounce) total in the whole pile of shells. I strongly suspect that the weight of feed (dry weight, before adding water moisture) for 100 birds is more like 3 kilograms (roughly 6 1/2 pounds) or maybe more... 34 grams x 100 is 3400 grams, which is 3.4 kg... if the feed weighs that much or more, he's adding 1% or less. The more the feed weighs, the lower percent of calcium it adds.
To bump up a 50lb bag of feed (22.73 kg) by 3.5% calcium, you would have to add 795 grams of calcium -- that's about 1 3/4 pounds of elemental calcium, which would be almost 2 kg (4.4 lb) of egg shells. That's the egg shells from about 284 eggs (almost 24 dozen eggs) added to the bag of feed. Every 81 egg shells increases the percent of calcium in the 50 lb bag by 1%.
Using metric units is MUCH easier here.
Here are two very cool articles about calcium and other nutrients in bugs and insects -- some favorite pea treats!
Insects are PACKED with protein and calcium, in case you are hungry...